The present invention relates to peptides derived from or based on bactericidal/permeability-increasing protein and therapeutic uses of such peptides.
Bactericidal/permeability-increasing protein (BPI) is a protein isolated from the granules of mammalian polymorphonuclear neutrophils (PMNs), which are blood cells essential in defending a mammal against invading microorganisms. Human BPI has been isolated from PMNs by acid extraction combined with either ion exchange chromatography (Elsbach, 1979, J. Biol. Chem. 254: 11000) or E. coli affinity chromatography (Weiss et al., 1987, Blood 69: 652), and has potent bactericidal activity against a broad spectrum of Gram-negative bacteria. The molecular weight of human BPI is approximately 55,000 daltons (55 kD). The complete amino acid sequence of human BPI, as well as the nucleotide sequence of DNA encoding BPI, have been elucidated by Gray et al., 1989, J. Biol. Chem. 264: 9505, incorporated herein by reference (see FIG. 1 in Gray et al.).
The bactericidal effect of BPI has been shown to be highly specific to sensitive Gram-negative species. The precise mechanism by which BPI kills Gram-negative bacteria is not yet known, but it is known that BPI must first attach to the surface of susceptible Gram-negative bacteria. This initial binding of BPI to the bacteria involves electrostatic interactions between BPI, which is a basic (i.e., positively charged) protein, and negatively charged sites on lipopolysaccharides (LPS). LPS is also known as "endotoxin" because of the potent inflammatory response that it stimulates. LPS induces the release of mediators by host inflammatory cells which may ultimately result in irreversible endotoxic shock. BPI binds to Lipid A, the most toxic and most biologically active component of LPS.
BPI is also capable of neutralizing the endotoxic properties of LPS to which it binds. Because of its Gram-negative bactericidal properties and its ability to bind to and neutralize LPS, BPI can be utilized for the treatment of mammals suffering from diseases caused by Gram-negative bacteria, including bacteremia, endotoxemia, and sepsis. These dual properties of BPI make BPI particularly useful and advantageous for such therapeutic administration.
A proteolytic fragment corresponding to the amino-terminal portion of human BPI possesses the LPS binding and neutralizing activities and antibacterial activity of the naturally-derived 55kD human holoprotein. In contrast to the amino-terminal portion, the carboxyl-terminal region of isolated human BPI displays only slightly detectable antibacterial activity (Ooi et al., 1991, J. Exp. Med. 174: 649). One BPI amino-terminal fragment, comprising approximately the first 199 amino acid residues of the human BPI holoprotein and referred to as "rBPI.sub.23 " (see Gazzano-Santoro et al., 1992, Infect. Immun. 60: 4754-4761) has been produced by recombinant means as a 23 kD protein. rBPI.sub.23 has been introduced into human clinical trials. Proinflammatory responses to endotoxin were significantly ameliorated when rBPI.sub.23 was co-administered with LPS.
Other endotoxin binding and neutralizing peptides are known in the art. One example is Limulus antilipopolysaccharide factor (LALF) from horseshoe crab amebocytes (Warren et al., 1992, Infect. Immunol. 60: 2506-2513). Another example is a cyclic, cationic lipopeptide from Bacillus polymyxa, termed Polymyxin B.sub.1. Polymyxin B.sub.1 is composed of six .alpha.,.gamma.-diaminobutyric acid residues, one D-phenylalanine, one leucine, one threonine and a 6-methyloctanoyl moiety (Morrison and Jacobs, 1976, Immunochem. 13: 813-818) and is also bactericidal. Polymyxin analogues lacking the fatty acid moiety are also known, which analogues retain LPS binding capacity but are without appreciable bactericidal activity (Danner et al., 1989, Antimicrob. Agents Chemother. 33: 1428-1434). Similar properties have also been found with synthetic cyclized polymyxin analogues (Rustici et al., 1993, Science 259: 361-365).
Known antibacterial peptides include cecropins and magainins. The cecropins are a family of antibacterial peptides found in the hemolymph of lepidopteran insects (Wade et al., 1990, Proc. Natl. Acad. Sci. USA 87: 4761-4765), and the magainins are a family of antibacterial peptides found in Xenopus skin and gastric mucosa (Zasloff et al., 1988, Proc. Natl. Acad. Sci. USA 85: 910-913). These peptides are linear and range from about 20 to about 40 amino acids in length. A less active mammalian cecropin has been reported from porcine intestinal mucosa, cecropin P1 (Boman et al., 1993, Infect. Immun. 61: 2978-2984). The cecropins are generally reported to be more potent than the magainins in bactericidal activity but appear to have less mammalian cell cytotoxicity. The cecropins and magainins are characterized by a continuous, amphipathic .alpha.-helical region which is necessary for bactericidal activity. The most potent of the cecropins identified to date is cecropin A. The sequence of the first ten amino acids of the cecropin A has some homology with the BPI amino acid sequence 90-99. However, the other 27 amino acids of cecropin A are clearly necessary for its bactericidal activity and there is little homology with BPI for those 27 amino acids. The magainins have even less homology with the BPI sequence.
Of interest to the present application are the disclosures in PCT International Application PCT/US91/05758 relating to compositions comprising BPI and an anionic compound, which compositions are said to exhibit (1) no bactericidal activity and (2) endotoxin neutralizing activity. Anionic compounds are preferably a protein such as serum albumin but can also be a polysaccharide such as heparin. In addition, Weiss et al. (1975, J. Clin. Invest. 5: 33-42) disclose that heparin sulfate and LPS block expression of the permeability-increasing activity of BPI. However, neither reference discloses that BPI actually neutralizes the biologic activities of heparin. Heparin binding does not necessarily imply heparin neutralization. For example, a family of heparin binding growth factors (HBGF) requires heparin as a cofactor to elicit a biological response. Examples of HBGF's include: fibroblast growth factors (FGF-1, FGF-2) and endothelial cell growth factors (ECGF-1, ECGF-2). Antithrombin III inhibition of clotting cascade proteases is another example of a heparin binding protein that requires heparin for activity and clearly does not neutralize heparin. Heparin binding proteins that do neutralize heparin (e.g., platelet factor IV, protamine, and thrombospondin) are generally inhibitory of the activities induced by heparin binding proteins that use heparin as a cofactor.
BPI (including aminoterminal fragments thereof) has a number of other important biological activities. For example, BPI has been shown to have heparin binding and heparin neutralization activities in copending and co-assigned parent U.S. patent application Ser. No. 08/030,644 filed Mar. 12, 1993 and continuation-in-part U.S. patent application Ser. No. 08/093,202, filed Jul. 15, 1993, the disclosures of which are incorporated by reference herein. These heparin binding and neutralization activities of BPI are significant due to the importance of current clinical uses of heparin. Heparin is commonly administered in doses of up to 400 U/kg during surgical procedures such as cardiopulmonary bypass, cardiac catherization and hemodialysis procedures in order to prevent blood coagulation during such procedures. When heparin is administered for anticoagulant effects during surgery, it is an important aspect of post-surgical therapy that the effects of heparin are promptly neutralized so that normal coagulation function can be restored. Currently, protamine is used to neutralize heparin. Protamines are a class of simple, arginine-rich, strongly basic, low molecular weight proteins. Administered alone, protamines (usually in the form of protamine sulfate) have anti-coagulant effects. When administered in the presence of heparin, a stable complex is formed and the anticoagulant activity of both drugs is lost. However, significant hypotensive and anaphylactoid effects of protamine have limited its clinical utility. Thus, due to its heparin binding and neutralization activities, BPI has potential utility as a substitute for protamine in heparin neutralization in a clinical context without the deleterious side-effects which have limited the usefulness of the protamines. The additional antibacterial and anti-endotoxin effects of BPI would also be useful and advantageous in post-surgical heparin neutralization compared with protamine.
Additionally, BPI is useful in inhibiting angiogenesis due in part to its heparin binding and neutralization activities. In adults, angiogenic growth factors are released as a result of vascular trauma (wound healing), immune stimuli (autoimmune disease), inflammatory mediators (Prostaglandins) or from tumor cells. These factors induce proliferation of endothelial cells (which is necessary for angiogenesis) via a heparin-dependent receptor binding mechanism (see Yayon et al., 1991, Cell 64: 841-848). Angiogenesis is also associated with a number of other pathological conditions, including the growth, proliferation, and metastasis of various tumors; diabetic retinopathy, retrolental fibroplasia, neovascular glaucoma, psoriasis, angiofibromas, immune and non-immune inflammation including rheumatoid arthritis, capillary proliferation within atherosclerotic plaques, hemangiomas, endometriosis and Kaposi's sarcoma. Thus, it would be desirable to inhibit angiogenesis in these and other instances, and the heparin binding and neutralization activities of BPI are useful to that end.
Several other heparin neutralizing proteins are also known to inhibit angiogenesis. For example, protamine is known to inhibit tumor-associated angiogenesis and subsequent tumor growth [see Folkman et al., 1992, Inflammation: Basic Principles and Clinical Correlates, 2d ed., (Galin et al., eds., Review Press, N.Y.), Ch. 40, pp. 821-839] A second heparin neutralizing protein, platelet factor IV, also inhibits angiogenesis (i.e., is angiostatic). Collagenase inhibitors are also known to inhibit angiogenesis (see Folkman et al., 1992, ibid.) Another known angiogenesis inhibitor, thrombospondin, binds to heparin with a repeating serine/tryptophan motif instead of a basic amino acid motif (see Guo et al., 1992, J. Biol. Chem. 267: 19349-19355).
Another utility of BPI involves pathological conditions associated with chronic inflammation, which is usually accompanied by angiogenesis. One example of a human disease related to chronic inflammation is arthritis, which involves inflammation of peripheral joints. In rheumatoid arthritis, the inflammation is immune-driven, while in reactive arthritis, inflammation is associated with infection of the synovial tissue with pyogenic bacteria or other infectious agents. Folkman et al., 1992, supra, have also noted that many types of arthritis progress from a stage dominated by an inflammatory infiltrate in the joint to a later stage in which a neovascular pannus invades the joint and begins to destroy cartilage. While it is unclear whether angiogenesis in arthritis is a causative component of the disease or an epiphenomenon, there is evidence that angiogenesis is necessary for the maintenance of synovitis in rheumatoid arthritis. One known angiogenesis inhibitor, AGM1470, has been shown to prevent the onset of arthritis and to inhibit established arthritis in collagen-induced arthritis models (Peacock et al., 1992, J. Exp. Med. 175: 1135-1138). While nonsteroidal anti-inflammatory drugs, corticosteroids and other therapies have provided treatment improvements for relief of arthritis, there remains a need in the art for more effective therapies for arthritis and other inflammatory diseases.
There continues to exist a need in the art for new products and methods for use as bactericidal agents and endotoxin neutralizing agents, and for heparin neutralization and inhibition of angiogenesis (normal or pathological). One avenue of investigation towards fulfilling this need is the determination of the functional domains of the BPI protein specifying each of these biological activities. Advantageous therapeutic embodiments would therefore comprise BPI functional domain peptides having one or more than one of the activities of BPI.